JP2003531729A - Efficient energy transfer capillaries - Google Patents

Abstract

(57) [Summary] A bonding tool for bonding fine wires to a substrate. The bonding tool includes a first cylindrical portion having a first diameter and a second cylindrical portion having a second diameter smaller than the first diameter and coupled to an end of the first cylindrical portion. A cylindrical portion (312); and a tapered portion (314) coupled to an end of the second cylindrical portion. The tapered portion has a third diameter substantially equal to a first diameter of the first cylindrical portion at a first end of the tapered portion. The apparatus further includes an axial tube extending along a longitudinal axis of the bonding tool from a first end of the bonding tool to a second end of the bonding tool.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION The present invention relates to tools used in bonding wires to semiconductor devices and, more particularly, to bonding tools having efficient ultrasonic energy transfer properties.

Description of Related Art Modern electronic devices rely heavily on printed circuit boards on which semiconductor chips, or integrated circuits (ICs), are mounted. Mechanical and electrical connections between the chip and the substrate have become a problem for chip designers. Three well-known techniques for interconnecting ICs to substrates are wire bonding, tape automated bonding (TAB) and flip chip.

The most common of these processes is wire bonding. In wire bonding, a plurality of bonding pads are arranged in a pattern on the upper surface of the substrate. A chip is placed in the center of the pattern of the bonding pad, and the upper surface of the chip faces away from the upper surface of the substrate. Fine wires (which can be aluminum wires or gold wires) are connected between contacts on the top surface of the chip and contacts on the top surface of the substrate. In particular, the connecting wires are fed and bonded to the chip and to the substrate through the capillaries (bonding tools described further below).

Capillaries are used to ball bond wires to electronic devices, especially bonding pads of semiconductor devices. Such capillaries are commonly formed from ceramic materials, primarily aluminum oxide, tungsten carbide, ruby, zircon reinforced alumina (ZTA), alumina reinforced zircon (ATZ) and other materials. Very fine wire (typically on the order of about 1 mil gold, copper or aluminum wire) passes through the axial tube of the capillary. The capillary has a small ball formed at the end of the wire, the ball being located outside the tip of the capillary. The first purpose is to bond this ball to a pad on a semiconductor device,
Next, the further part along the wire is bonded to a lead frame or the like. During the bonding cycle, the capillary performs more than one function.

Once the ball is formed, the capillary first centers the ball partially within the capillary to target the bonding pad. The ball is bonded to a pad on the semiconductor device by the first bonding step. When the capillary contacts the ball on the bonding pad, the ball
Crush and flatten. Since the bond pad is typically made of aluminum, a thin oxide forms on the surface of the bond pad. In order to form a proper bond, it is preferable to break the oxide surface to expose the aluminum surface. An effective way to break the oxide is to "polish" the surface of the oxide with wire balls. The wire balls are placed on the surface of the aluminum oxide and the capillaries immediately move in a linear direction based on the expansion and contraction of piezoelectric elements placed in the ultrasonic horn in which the capillaries are mounted.
The rapid motion, in addition to the heat applied to the bond pad, creates an effective bond by moving molecules between the wire and the bond pad.

The capillary then wraps the bonding wire both outside the capillary and again inside the capillary, treating the wire while providing a smooth feed. The capillaries are then "stitch" bonded and "tucked".
Form a bond or "tail" bond.

Thermosonic wire bonding is currently the process of another means for interconnecting semiconductor devices to a supporting substrate. The thermosonic bonding process is partially based on the transfer of ultrasonic energy from a transducer attached to a movable bonding head, through a tool (eg, capillary or wedge), to a ball or wire welded to a semiconductor device or supporting substrate. Depends on.

In conventional capillaries (bonding tools), the geometry of the bonding tool is not designed to improve the transfer of energy to the contact area of the ball / wire interconnect pad. The inventors of the present invention have found that controlling the ultrasonic attenuation of stress / strain waveforms exerted on the tool due to the ultrasonic transducer is important for controlling the bonding process and thus its performance.

However, conventional bonding tool designs are deficient because they are based on interconnect width and wire bond loop height and do not take into account ultrasonic attenuation control. As such, conventional bonding tools are not energy efficient.

FIG. 1 shows a diagram of a conventional bonding tool. As shown in FIG. 1, the bonding tool 100 has a cylindrical body portion 102 and a tapered portion 104. An axial tube 108 extends from the end 110 of the bonding tool 100 to the tip 106. Bonding wires (not shown) pass through axial tube 108 to tip 106 and ultimately bond onto a substrate (not shown).

SUMMARY OF THE INVENTION In order to overcome the above mentioned drawbacks of conventional bonding tools, the present invention relates to an energy efficient bonding tool for bonding fine wires to a substrate.

The bonding tool has a first cylindrical portion having a first diameter and a second cylindrical portion having a second diameter smaller than the first diameter, and a second cylindrical portion joined at an end of the first cylindrical portion. A cylindrical part,
A tapered portion coupled to an end of the second cylindrical portion.

[0013]   According to one aspect of the present invention, the second cylindrical portion is a groove.

[0014]   According to another aspect of the present invention, the second cylindrical portion is a plurality of grooves.

[0015]   According to a further aspect of the invention, the groove has a substantially rectangular cross section.

[0016]   According to another aspect of the invention, slots are used instead of grooves.

According to yet another aspect of the present invention, the tapered portion is directly adjacent to the second cylindrical portion.

These and other aspects of the invention are set forth below with reference to the accompanying drawings and description of exemplary embodiments of the invention.

The invention is best understood from the following detailed description when read with the accompanying drawing figures. It should be emphasized that, according to common practice, the various features in the drawings are not to scale. On the contrary, the sizes of the various features may be arbitrarily expanded or reduced for clarity.

DETAILED DESCRIPTION The present invention overcomes the shortcomings of conventional capillary bonding tools by varying the mass distribution along the length of the bonding tool. The resulting bonding tool requires less ultrasonic energy to form the bond on the substrate when compared to conventional bonding tools.

Ultrasonic bonding tool design can be accomplished by mathematically describing the movement of the tool driven by an ultrasonic transducer. Such a system is represented by a cantilever beam as shown in equation (1).

[0022]

[Equation 1] Here, E is the elastic coefficient, I is the moment of inertia, m is the mass distribution, z is the distance from the moving support, x is the amount of displacement perpendicular to the beam, and x ₀ is the movement of the moving support.

FIG. 2 shows the response of the bonding tool according to equation (1). As shown in FIG. 2, in designing the bonding tool, the cantilever beam 200 represents the bonding tool, 204 represents the movement x _{0 of the} transducer 202, and 206 represents the response movement x (z, t) of the bonding tool. Since the mass and moment of inertia can change along the beam, these parameters are used to design the bonding tool configuration and "shape" to produce the desired bonding ultrasonic motion.

As mentioned above, in the conventional design, the moment of inertia I and the mass distribution m are not controlled for the purpose of ultrasonic damping, but allow the required interconnection width and wire bonding loop height. Is strictly controlled to. In an exemplary embodiment of the invention, cross-sectional shape and mass distribution are specified to control ultrasonic attenuation.

Some examples of engineering effects (geometric moment of inertia (Area Momen)
3 shows tof Inertia) I and mass distribution m). Table 1 shows FIGS.
With reference to B, we summarize the experimental results related to confirming this concept of groove-like geometry. However, the invention is not limited to this shape and contemplates the use of other geometric shapes.

[0026]

[Table 1] FIG. 3A illustrates a bonding tool 300 according to the first exemplary embodiment of the present invention.
FIG. As shown in FIG. 3A, the bonding tool 300 has a cylindrical upper body portion 302 and a cylindrical lower body portion 304. The lower body portion 304 has a cylindrical portion 308 and a conical portion 306, and the lower body portion 304 extends from the cylindrical portion 306 to the tip 310 of the bonding tool 300. A groove 312 is arranged between the upper body 302 and the lower body 304. The groove 312 is located at a distance 314 between about 0.1490 inch and 0.1833 inch (3.785 to 4.656 mm) on the tip 310. The groove 312 is fitted from the upper and lower body parts such that the groove 312 has a diameter 318 of between about 0.0083 inch and 0.0155 inch (0.211 to 0.394 mm). The height 316 of the groove 312 is between about 0.0136 inch and 0.0200 inch (0.345 to 0.508 mm).

FIG. 3B is a side view of the cross section of the bonding tool 300. As shown in FIG. 3B, the axial tube 320 extends from the end 322 of the bonding tool 300 to the tip 310. In the exemplary embodiment, axial tube 320 has a substantially continuous tapered shape with a predetermined angle 326 of about 14 °. However, the present invention is not limited to this shape, and it is also contemplated that the axial tube 320 may be tapered over a substantially constant diameter or only a portion of the length of the bonding tool 300. If the latter case is desired, insertion of the wire at the upper end 322 of the bonding tool 300 can be facilitated.
An example of such another axial tube is shown in FIGS. 3C and 3D. As shown in FIG. 3C, the axial tube 320 has a diameter 330 that is substantially constant along the length of the bonding tool 300. In FIG. 3D, the holes 320 represent the bonding tool 30.
It has a substantially constant diameter 340 along a portion of its length of zero and a taper 342 adjacent the end 322 of the bonding tool 300.

In order to maintain the structural integrity of the bonding tool 300, the distance between the groove 312 and the hole 320 should be taken into consideration when designing the bonding tool 300. We call this distance the "minimum wall thickness" (MWT) 324. Next in FIG.
Referring to FIG. 3, an enlarged cross-sectional view of the bonding tool 300 is shown. This figure is NW
T324 is shown in detail. As shown in FIG. 4, the groove 312 may have a radius 402 inside the slot 312. This is mainly due to the shape of the device used to form the groove 312. It is contemplated that the groove 312 may be formed using a blade, such as a saw tooth. The formation of the groove 312 is not limited to this, and may be formed by using another conventional method such as lapping or molding.

Referring again to FIG. 3A, in the preferred embodiment of the present invention, distance 314 is approximately zero.
It may be between .140 and 0.143 inches (3.556 and 3.632 mm), and the height 316 is approximately 0.0160 and 0.0190 inches (0.406 and 0.483 mm).
) And the diameter 318 is about 0.0154 to 0.0160 inches (0.39).
1 to 0.406 mm) and the MWT 324 is greater than 0.098 inches. In the most preferred embodiment of the invention, distance 314 is about 0.142 inches (3.61 mm) and height 316 is about 0.0170 inches (0.432 mm).
), The diameter 318 is about 0.0157 inches (0.399 mm), and the MW
The T324 is approximately 0.0100 inches (0.254 mm).

Referring to FIG. 5, a graph 500 is shown. In FIG. 5, graph 500 shows displacement 2 (shown in FIG. 2) of bonding tool 300 due to the application of an ultrasonic waveform.
The effect of groove 312 based on 06 is plotted. The graph 500 is plotted along the length of the bonding tool 300 from the transducer pedestal (not shown) to the free bonding end (tip 310). In FIG. 5, the horizontal axis represents the position (inch) from the lower portion of the transducer, and the vertical axis represents the displacement (μm) of the bonding tool. The graph 500 is plotted for various bonding tools that differ in the location and geometry of the groove 312. In FIG. 5, the position of the zero displacement tool motion caused by the ultrasonic energy at the fixed frequency is represented by node 5
Shown as 02. In the present invention, the groove 312 of the bonding tool 300 is arranged at the node 502. The inventor has found that placing the groove 312 in the node 502 maximizes the efficiency of the bonding tool. In FIG.
Plot 504 shows the response of a conventional (reference) bonding tool and plots 506-518 show the response of a bonding tool according to an exemplary embodiment of the invention.

In FIG. 6, a graph 600 plots ultrasonic energy versus resonant frequency for a fixed tool tip displacement. In FIG. 6, resonance points 602 to 6
24 is shown and is plotted as curve 626. As shown in FIG. 6, point 624 represents a conventional reference tool, which exhibits even greater energy requirements when compared to the tool according to the present invention (shown as points 602-622). Graph 60
Zero indicates a significant reduction in energy demand due to the location of the groove 312 in the bonding tool 300.

In FIG. 7, a graph 700 plots the displacement of a bonding tool according to the present invention and a conventional bonding tool. As shown in FIG. 7, the displacement amount of the bonding tool having a geometrical shape optimized by machining the groove by controlling the geometrical moment of inertia I is equal to that of a standard shank (no groove) bonding tool. Greater than displacement. Considering FIG. 7, for wire bonding, the tip displacement plots show standard bonding tools both before (curve 702) and after use (curve 704) of the controlled geometry capillary of the present invention. (
It is larger than the displacement of curve 706).

The inventor has also found that the lower energy requirement of the exemplary bonding tool results in higher quality bonding. Table 2 summarizes data showing various bonding tools, bond (ultrasonic) energy, bond strength and shear force required to break the bond. As clearly shown, using less than 50% of the energy of conventional bonding tools, the exemplary bonding tool provides a bond that exhibits better shear resistance than conventional.

[0034]

[Table 2] Table 3 summarizes the data showing the excellent tensile resistance of the bond formed by the bonding tool according to the present invention compared to the conventional bonding tool.

[0035]

[Table 3] FIG. 8 is a partial side view of the second exemplary embodiment of the present invention. In FIG. 8, the groove 312 includes a curved contour 802. In all other respects, the second exemplary embodiment is similar to the first exemplary embodiment.

FIG. 9 is a partial side view of the third exemplary embodiment of the present invention. In FIG. 9, the groove 312 of the bonding tool 300 includes two grooves 902 and 904.
Although two grooves are shown in FIG. 9, the invention is not so limited and may include more than two grooves if desired. In the exemplary embodiment, each groove has a curved portion 910. As described above with respect to the first exemplary embodiment, the contours of the grooves 902, 904 depend on the process used to form the grooves and need not include curved portions. In FIG. 9, edges 906, 908 may be chamfered or chamfered if desired to remove sharp edges resulting from the formation of grooves 902, 904. In all other aspects, the third exemplary embodiment is similar to the first exemplary embodiment.

10A and 10B are a partial side view and a partial plan view, respectively, of a fourth exemplary embodiment of the present invention. 10A-C, slot 1000 is applied in place of groove 312 in bonding tool 300. Slot 100
The width 1002, length 1004, depth 1006 and number of zeros are based on the desired response of the bonding tool 300. The slot may be substantially parallel to the longitudinal axis of the bonding tool, or it may be positioned in the body of the bonding tool 300 at a predetermined angle, as shown in Figure 10C. In all other respects, the fourth exemplary embodiment is similar to the first exemplary embodiment.

FIG. 11 is a side view of the fifth exemplary embodiment of the present invention. In FIG. 11, the tapered portion 308 is directly adjacent to the groove 312. In all other respects, the fifth
The exemplary embodiment of is similar to the first exemplary embodiment.

Although the present invention has been described with reference to exemplary embodiments, it is not limited thereto. Rather, the appended claims are intended to cover various modifications and embodiments of the present invention that may be made by those skilled in the art without departing from the true spirit and scope of the present invention. is there.

[Brief description of drawings]

[Figure 1]   FIG. 1 is a side view of a conventional bonding tool.

FIG. 2 is a diagram showing the response of a bonding tool with respect to transducer movement.

FIG. 3A   FIG. 3A is a diagram of a bonding tool according to an exemplary embodiment of the present invention.

FIG. 3B   FIG. 3B is a diagram of a bonding tool according to an exemplary embodiment of the present invention.

[Fig. 3C]   FIG. 3C is a diagram of a bonding tool according to an exemplary embodiment of the present invention.

[Fig. 3D]   FIG. 3D is a diagram of a bonding tool according to an exemplary embodiment of the invention.

[Figure 4]   FIG. 4 is an enlarged sectional view of an embodiment of the present invention.

FIG. 5 is a graph plotting the effect of ultrasonic energy on a bonding tool according to an exemplary embodiment of the present invention.

FIG. 6 is a graph plotting ultrasonic energy versus resonant frequency for a bonding tool according to an exemplary embodiment of the present invention.

FIG. 7 is a graph plotting displacement of capillaries of a bonding tool according to an exemplary embodiment of the present invention.

FIG. 8 is a partial side view of a bonding tool according to a second exemplary embodiment of the present invention.

FIG. 9 is a partial side view of a bonding tool according to a third exemplary embodiment of the present invention.

FIG. 10A is a diagram of a bonding tool according to a fourth exemplary embodiment of the present invention.

FIG. 10B is a diagram of a bonding tool according to a fourth exemplary embodiment of the present invention.

FIG. 10C is a diagram of a bonding tool according to a fourth exemplary embodiment of the present invention.

FIG. 11 is a partial side view of a bonding tool according to a fifth exemplary embodiment of the present invention.

─────────────────────────────────────────────────── ─── 【Continued summary】

Claims (30)

[Claims] 1. A bonding tool for bonding a fine wire to a substrate, comprising: a first cylindrical portion having a first diameter; and a second diameter smaller than the first diameter. A bonding tool comprising: a second columnar portion coupled to an end of the first columnar portion; and a taper portion coupled to an end of the second columnar portion. 2. The tapered portion has a third diameter at the first end of the tapered portion that is substantially equal to the first diameter of the first cylindrical portion. Bonding tools. 3. The method of claim 1, further comprising an axial tube extending along a longitudinal axis of the bonding tool from a first end of the bonding tool to a second end of the bonding tool. Bonding tools. 4. The axial tube has a first diameter at a first end of the first cylindrical section and a second diameter at a tip of the tapered section, the first tube having a first diameter. The bonding tool according to claim 3, wherein the diameter is larger than the second diameter. 5. The bonding tool of claim 1, wherein the bonding tool is formed from at least one of the group consisting of aluminum oxide, tungsten carbide, ruby, ceramic and zircon. 6. A bonding tool for bonding a fine wire to a substrate, comprising: a first cylindrical portion having a first diameter; and a taper portion coupled to an end of the first cylindrical portion. A bonding tool comprising: a groove disposed between the first cylindrical portion and the tapered portion. 7. The groove is located at a node of the bonding tool,
The bonding tool according to claim 6. 8. The bonding tool according to claim 6, wherein the groove is arranged at a predetermined distance from an end of the tapered portion. 9. The distance is about 0.1400 to 0.1833 inches (3.5 inches).
The bonding tool according to claim 8, which is between 56 and 4.656 mm). 10. The distance is about 0.1400 to 0.1430 inches (3.
The bonding tool according to claim 8, which is between 556 and 3.632 mm. 11. The bonding tool according to claim 6, wherein the groove has a predetermined width. 12. The width is about 0.0136 to 0.0200 inches (0.3 inches).
The bonding tool according to claim 11, which is between 45 and 0.508 mm). 13. The width is approximately 0.0160 to 0.0190 inches (0.4
Bonding tool according to claim 11, which is between 06-0.483 mm). 14. The bonding tool according to claim 6, wherein the groove has a predetermined diameter smaller than the first diameter of the cylindrical portion. 15. The diameter is about 0.0082 to 0.0156 inches (0.
The bonding tool according to claim 14, which is between 208 and 0.396 mm). 16. The diameter is about 0.0154 to 0.0160 inches (0.
Bonding tool according to claim 14, which is between 39 and 0.406 mm). 17. A first having a first diameter, a first end, and a second end.
A second cylindrical portion having a second diameter smaller than the first diameter and coupled to the second end of the first cylindrical portion; A tapered portion having a first end and a second end coupled to an end of the portion, the first end of the tapered portion being the first of the first cylindrical portions. A tapered portion having a third diameter substantially equal to the diameter of the first end, the second end having a fourth diameter smaller than the third diameter, and the first cylindrical portion of the first cylindrical portion. An axial tube extending from one end to the second end of the taper portion. 18. The capillary bonding tool of claim 17, wherein the axial tube has a conical shape. 19. The axial tube has a substantially constant diameter.
7. The capillary bonding tool according to 7. 20. The capillary bonding tool of claim 19, wherein the axial tube has a taper located at the first end of the first cylindrical section. 21. A bonding tool for bonding a fine wire to a substrate, comprising: a first cylindrical portion having a first diameter; and a taper portion coupled to an end of the first cylindrical portion. A bonding tool comprising a hole disposed between the first cylindrical portion and the tapered portion. 22. The bonding tool according to claim 21, wherein the hole is at least one groove. 23. The bonding tool of claim 22, wherein the groove has a substantially rectangular cross section. 24. The bonding tool of claim 23, wherein the groove has a radius along at least a portion of the cross section. 25. The bonding tool according to claim 21, wherein the hole is a plurality of grooves. 26. The bonding tool of claim 21, wherein the holes are slots. 27. The bonding tool according to claim 26, wherein the slot is a plurality of slots arranged along an outer periphery of the bonding tool. 28. The bonding tool of claim 26, wherein the slot has a longitudinal axis that is substantially parallel to the longitudinal axis of the bonding tool. 29. The bonding tool of claim 26, wherein the slot has a longitudinal axis that is offset from the longitudinal axis of the bonding tool by a predetermined angle. 30. A bonding tool for bonding a fine wire to a substrate, which has a first cylindrical portion having a first diameter and a second diameter smaller than the first diameter. A second columnar part coupled to the end of the first columnar part, a third columnar part having the first diameter, and a taper part coupled to the end of the third columnar part. Bonding tool.